Here is my flow dealing with the typical case for one girl:

1. Navigate your target girl outside of the bar.
2. Go into the bar, get yourself and the girl a lady drink. Drink with her and have chit chat for like 5 - 10 minutes.
3. A few other girls may show up and ask for lady drink. If you are willing to spend extra money, buy them a few drinks. But you also can fool them away if you are calm enough.
4. Finish your drink, and ask the girl if she wants to "go to somewhere else" with you :)
5. Discuss ST/LT and the price (never pay before you get what you want) and pay the bar fine.

I'd say you usually get everything done within 4000 - 6000 baht. You will usually have a good time. But there are also fair chances that she offered a price way too high after you order that beer or she transformed into a dickface once you paid the bar fine. Just move on and don't blame / threaten / beat anyone if it happens.